Since the USPS specifies that a Tracking barcode/number appear on items such as Priority, First Class Mail Packages, and Parcel Select,
the Label 400 is recommended for whenever a standard printed USPS shipping label is not present.

Noting that a number of USPS services now have the service as a built-in, at no fee incurred. And as a result of the change, you should
notice, for example, the assigned USPS Tracking number appear on the receipt of a First Class Parcel being sent, for your convenience.